Linear hydroxyaryl-functional polydiorganosiloxanes are useful starting materials for making polydiorganosiloxane-polyorgano block copolymers. These block copolymers are known to have many unique properties and useful applications. For example, polydimethylsiloxane-polycarbonate block copolymers exhibit good low temperature impact resistance, making them useful materials for the manufacture of helmets.
There are two general pathways known to prepare polydiorganosiloxane-polyorgano block copolymers from linear hydroxyaryl-functional polydiorganosiloxanes. Linear hydroxyaryl-functional polysiloxanes react with bisphenolic compounds or their polycarbonate, polyester, polyetherimide, polyether ether ketone, or polysulfone oligomers and a polycarbonate precursor under the conditions of a two-phase boundary polycondensation process. Alternatively, linear hydroxyaryl-functional polysiloxanes react with bisphenolic compounds or their polycarbonate, polyester, polyetherimide, polyether ether ketone, or polysulfone oligomers and a diorganocarbonate or an organic diester in a solventless, transesterification melt process. Both processes lead to block copolymers, wherein the polysiloxane block is bonded to the polyorgano block by either a carbonate or an ester linkage.
The aforementioned processes that employ the two-phase boundary polycondensation process in the preparation of polysiloxane-polyorgano block copolymers have the disadvantage that this process requires the use of large amounts of organic solvents or highly toxic phosgene. Furthermore, the preferred solvents in the two-phase boundary polycondensation process are halogenated hydrocarbons or halogenated aromatics, such as dichloromethane or chlorobenzene. Handling of large amounts of these solvents is undesirable for environmental, health and safety reasons. The solventless melt process for the preparation of polysiloxane-polyorgano block copolymers has the advantage of requiring no solvents and fewer or no subsequent purification steps. It is, therefore, advantageous that the polysiloxane used in the preparation of said block copolymers by the solventless melt process be free of unwanted impurities that could be detrimental to the properties of the resulting block copolymers. Non-limiting examples of such unwanted impurities are strong bases, inorganic salts, such as in particular the salts of hydroxy or halogen ions, amines and heavy metals. Accordingly there is a need for linear hydroxyaryl-terminated polydialkylsiloxanes of controlled structure that are free of unwanted impurities.
Furthermore, the solventless melt process to polysiloxane-polyorgano block copolymers is an inherently biphasic system, wherein even after formation of the block copolymers the siloxane portion builds a distinct disperse phase. It was found that highly pure hydroxyaryl-terminated polysiloxanes exhibit poor reactivity in the solventless melt process, in particular in the reaction with polycarbonate, polyester, polyetherimide, polyether ether ketone, or polysulfone oligomers, even in the presence of known transesterification catalysts, leading to excessively long reaction times and added costs. This poor reactivity is particularly undesirable in continuous melt processes, such as in an extrusion process according to U.S. Pat. No. 6,506,871. Adding excessive amounts of known transesterification catalysts to increase reactivity is undesirable, as the resulting high levels of catalyst residues can have detrimental effects on the properties of the block copolymers. Accordingly, there remains the need for a solventless melt process of high reactivity, employing low levels of catalysts, and providing for polysiloxane-polyorgano block copolymers with optimal properties.
U.S. Pat. Nos. 3,189,662 and 3,328,350 describe the reaction of chloro-terminated polysiloxanes with bisphenolic compounds and phosgene to form polysiloxane-polycarbonate block copolymers, eliminating hydrochloric acid as the byproduct. This process has the disadvantages of requiring the use of large amounts of a basic compound to neutralize the hydrochloric acid byproduct and a tedious filtration to remove the large amount of resulting salt.
U.S. Pat. Nos. 4,584,360 and 4,732,949 describe the reaction of bisphenolic compounds with α,ω-bisacyloxypolydimethylsiloxanes to form hydroxyaryloxy-terminated polyorganosiloxanes. In a subsequent step the hydroxyaryloxy-terminated polysiloxane is reacted with the excess bisphenolic compound and a carbonate precursor, such as phosgene, and stoichiometric amounts of an inorganic base, under the conditions of the two-phase boundary polycondensation process, to form block copolymers. According to the '360 and the '949 patents, the preferred inorganic bases are alkali metal and alkaline earth metal carbonates.
In order to dissolve the large excess of bisphenolic compounds used, the process disclosed in the '360 and the '949 patents requires the use of large amounts of organic solvents, typically chlorinated organic solvents. Removal of the large amounts of solvents by distillation increases manufacturing costs. Furthermore, the base used in the reaction mixture forms salts, which are difficult to be completely removed from the block copolymer product. Similarly, isolation of hydroxyaryloxy-terminated siloxanes according to these processes in a pure form which are free of undesirable impurities is tedious and costly.
U.S. Pat. Nos. 3,442,854, 5,319,066, 5,340,905, 5,399,659, 5,412,061, 6,506,871, 6,753,405 describe methods for preparing thermoplastic polycarbonate polymers by a solventless melt process, wherein the catalysts are employed. U.S. Pat. Nos. 5,227,449, 5,504,177, 5,783,651, 8,466,249, 8,829,140 describe methods for preparing polysiloxane-polycarbonate blockcopolymers by a solventless transesterification processes.
U.S. Pat. No. 5,126,495 describes polyester-polycarbonate-polysiloxane triblock copolymers starting from hydroxyaryloxy-functional polysiloxanes.
U.S. Pat. No. 6,066,700 describes a process for preparation of polysiloxane-polycarbonate block copolymers by solventless melt transesterification comprising reacting an oligocarbonate and a hydroxyaryloxy-functional siloxane in the presence of a catalyst.
The inventors found surprisingly that the presence of certain levels of inorganic and/or organic salts in the polysiloxane polymer prior to the formation of the reaction mixture with the polyorgano oligomers result not only in an improved reactivity but also in polysiloxane-polyorgano copolymers of improved properties in particular good melt stability, improved solvent and hydrolysis stability and improved low temperature impact resistance. It is especially remarkable, that high yields of copolymer formation are achieved with very low levels of said salts in particularly short reaction times. It is equally remarkable, that said salts do not negatively impact the melt stability of the copolymer.